Free piston engine starting apparatus

ABSTRACT

Apparatus and method features are disclosed for starting free piston engines, and particularly for initiating combustion on the first power stroke of such an engine or on a recycled starting stroke. Such an initial power stroke is achieved by spark ignition of a suitable mixture in a combustion chamber of the free piston engine, preferably in the power cylinder. The first combustion is obtained at a pressure relatively lower than the compression ratio used for combustion during normal operation. Thus one may even use a negligible compression within such chamber to provide a first power stroke which initiates movement of the engine, but which provides substantially less dirving force than that which is provided by a regular power stroke once such an engine is running.

United States Patent [191 Braun Nov. 6, 1973 FREE PISTON ENGINE STARTINGAPPARATUS Related [1.8. Application Data [63] Continuation of Ser. No.66,386, Aug. 24, 1970,

abandoned.

[52] U.S. Cl. 123/46 A, 123/46 R, 123/46 SC, '123/179 BG, 123/179 R,60/14, 60/DIG. l [51] Int. Cl. F021) 71/02 1 [58] Field of Search 123/46A, 46 R, 46 B, 123/46 SC, 179 R, 179 B6; 60/14, 14 B, 17,

' DIG. l

[56] I References Cited 7 UNITED STATES PATENTS 929,696 8/1909 Oberly123/46 R 1,732,694 10/1929 Pescara 123/46 R 2,423,720 7/1947 Mullesanset al. 123/46 R 2,434,877 H1948 Welsh et al. 123/46 R 2,462,745 2/1949Horgen 123/46 R 2,983,098 5/1961 Bush .3. l23/46R 2,918,788 12/1959Wachsmuth 60/14 13 3,071,120 l/l963 McCrory et al 123/46 R 2,982,2715/1961 Heintz 123/46 A Primary ExaminerWendell E. BurnsAttorney-Frederick E. Lange et a1.

[57] ABSTRACT Apparatus and method features are disclosed for startingfree piston engines, and particularly for initiating combustion on thefirst power stroke of such an engine or on a recycled starting stroke.Such an initial power stroke is achieved by spark ignition of a suitablemixture in a combustion chamber of the free piston engine, preferably inthe power cylinder. The first combustion is obtained at a pressurerelatively lower than the compression ratio used for combustion duringnormal operation. Thus one may even use a negligible compression withinsuch chamber to provide a first power stroke which initiates movement ofthe engine, but which provides substantially less dirving force thanthat which is provided by a regular power stroke once such an en glue isrunning.

17 Claims, 3 Drawing Figures PAIENTEnNnv s 1915 SHEET 10F 2 INVENTOR.

ATTOQAJESJ PMENIEUImv 5 I973 SHEET 2 OF 2 INVENTOR.

mmw

FREE PISTON ENGINE STARTING APPARATUS This is a continuation ofapplication Ser. No. 66,386, filed Aug. 24, 1970 now abandoned. I

The starting features are preferably combined with improved features formaking a gradual transition from the initial or first combustion to anormal running condition. This transition is facilitated by controllingcombustion during this transitional stage in response to amovement-related characteristic or parameter of the power piston, suchas its velocity or rate of change of position in the power cylinder .ofthe engine. Thus, combustion is caused to occur at'a desired time whichis related to the time the power system reverses direction at the startof a power stroke, without regard to variations from one stroke toanother: in the actual physical position of the power piston along itspath of movement in the cylinder at the moment of piston reversal. Theoriginal relatively low compression takes place at a position of thepower piston where the various inlet and exhaust ports'are at leastsubstantially closed, i.e., substantially before the normal innerreversal point of the power piston movement. By utilizing amovement-related power piston characteristic to control ignition on atleast the transitional strokes subsequent to the first starting stroke,the chances of successful transition to a normal running condition areincreased. Thus each subsequent combustion is timed close to the momentof reversal of the power piston, both during the gradually increasingtransitional strokes. and then during the ultimate normal running powerstrokes of the engine. I

Features are also disclosed for moving the power piston for the startingcombustion, for providing a suitable combustible mixture for the firstpower stroke, and for providing a combination of combustion-causingpossibilities in which combustion may be initiated in timed relation tothe moment of piston reversal for most operations, but in whichposition-responsive ignition means,

i.e., means actuated when the power piston reaches a particular physicalposition, may be used to initiate combustion at selected strokes, suchas'a first starting stroke, or a later transitional or running stroke.

I BACKGROUND OF THE INVENTION 'latched, it has been known to utilize aseparate source of air pressure to build up substantial pressure in acompressor or bouncer chamber against one face of a compressor orbouncer piston in such a direction as to urge the piston through itspower section compression stroke. By releasing the latched pistonassembly, this extra pressure quickly drives the piston through thecompression stroke, hopefully .with enough force to achieve-either thehigh degree'ofcompression in the power cylinder combustion chamber whichis necessary for compression ignition of a diesel engine or the somewhatlower but still very substantial'compression ratios customarily reachedat the point of spark ignition for operation of a spark ignition engine.1

'Some of these prior artfstarting devices, instead of latching the powerpiston assembly in one position and then releasing it suddenly, whileunder high pressure, have provided devices in which successive pulses ofhigh pressure air in a bouncer or other chamber cause the free piston tocycle back and forth at gradually increasing stroke lengths andgradually increasing combustion chamber pressures, until finally thecombustion chamber pressure is high enough to obtain a compression ofspark ignition at an inner reversal or top dead point which correspondsvery closely to the normal reversal point of the power piston duringregular running conditions.

Those devices which include a latching arrangement for the power pistoninvolve a sudden release of substantial force, all of which has apossibility of damage to the parts. Each of the prior art startingarrangements just discussed and others also require very substantialamounts of high pressure air in order to achieve the high level ofcompression in the combustion chamber which is required for normalignition.

Moreover these prior art devices operate on a sort of all or nothingbasis. Either the first ignition and power stroke is sufficient to getthe engine close to normal running operation or another start must betried. There is no satisfactory provision for gradual build up ofsuccessive power strokes through a transitional range in which a poorfirst stroke or a misfire prevents the achievement ofnormal runningconditions.

SUMMARY OF THE PRESENT INVENTION The present invention providesapparatus and method features for achieving the initial power stroke ina single acting free piston engine under circumstances which do notrequire high compression in the combustion chamber and which do notrequire the use of large amounts of compressed air for the startingcycle. In its broadest aspect,-the invention includes the provision of acombustible mixture, suitable for spark ignition at a pressure which iseither relatively close to the ambient or atmospheric pressure or atleast substantiallybelowv the high compression ratio normally usedduring operation. This mixture is fed into the combustion chamber, thepower piston is moved to a position in which at least the inlet ports ofthe power cylinder are substantially closed and the mixture is ignitedbysa spark. The resulting combustion drives the power piston outwardlytoward its outer dead point or reversal position, from which it will bereturned for a subsequent compression stroke by the usual sources ofreturn energy in such a single-acting free piston engine, i.e., thepressure developed in a bounce chamber, the pressure developed in theclearance volume of the compressor, or a combination of these or othersimilar forces.

While it is possible that such an initial low compression power strokemight generate sufficent return energy to bring the power piston back toa physical position within the power cylinder at which thepositionresponsive timing means of prior art engines might be effective'to cause further combustion and a relatively rapid transition to normalrunning conditions, the invention further provides for gradualtransitional adjustment of the timing of the combustion-causing means.Such adjustment can be made manually. However, the preferred embodimentof the present invention combines thefurther feature of automaticallycontrolling at least the subsequent transitional ignition or combustionpoints in a predeterminable time relationship to the moment at which thepower piston reverses direction at the end of such a transitionalcompression stroke, without regard to variations in the actual physicalposition of the power piston within its cylinder at the moment of suchreversal. Thus, if the force generated in the initial startingcombustion stroke is only sufficient so that the power piston returns toa point substantially short of the normal desired inner reversal pointfor regular operations, the second combustion stroke will be initiatedin response to a movement-related characteristic of the power pistonwhich has a predeterminable time relationship to the moment of powerpiston reversal at the start of a power stroke This will provide asecond power stroke. in a situation where the normal position-responsiveignition means of the prior art might not even be actuated. According tothe present invention, the initiation of combustion close to the momentof power piston reversal at each successive transitional stroke, assuresa gradually increasing build up from the initial starting power stroke,untilthe power piston finally reciprocates through a full normal runningstroke.

A preferred embodiment of apparatus according to the present inventionbriefly includes sensing means which is responsive to a movement-relatedpower piston characteristic or parameter which has a predeterminablerelationship to the moment when the power piston reaches a reversalpoint at the end of each compression stroke and which is substantiallyindependent of variations in the actual physical position of the powerpiston along its path within the cylinder at the moment of pistonreversal for different power strokes. This sensing means provides asensing signal analogous to the instantaneous values of the selectedmovementrelated power piston characteristic. The sensing signal is fedto a control means which in turn actuates the combustion-causing meansat the desired moment in time related to the piston reversal. Thecontrol means may include adjustable timing or time-delay means to varythe desired time relationship between the actuation of thecombustion-causing means andthe moment of piston reversal at the end ofthe compression stroke.

Although the preferred form of the invention includes the combination ofmethod and apparatus features just described, it will be understoodthatthe starting method and-apparatus have broad application and that thespark ignition of a charge of combustible gas at pressure substantiallybelow normal compression or spark ignition pressure as a means ofachieving the first starting movement of a single-acting free pistonengine is capable of broader application with other methods andapparatus for controlling combustion during the transition from start-upto normal running conditions. This transition can even be made manuallyby suitable adjustment of the ignition point from the position at whichthe starting ignition occurs toward points successively closer to thedesired top dead point or reversal point of the piston during normalrunning operation.

The present invention further provides a combination of reversal-relatedcombustion causing means and position-responsive combustion causingmeans. Thus in one embodiment, the initial ignition for the firststarting stroke may be responsive to the arrival of the power piston ata specific desired position, while combustion for subsequenttransitional power strokes is caused by reversal-related ignition means.The reversal-related means in this embodiment is also preferably used tocontrol combustion during normal operation.

In another embodiment, reversal-related ignition apparatus is soconstructed that it can cause both the initial starting combustion, andthe combustion for subsequent transitional power strokes. A separatepositionresponsive combustion-causing means may also be provided in thisembodiment to supplement the action of the reversal-related ignitionapparatus.

With such a combination, ignition may be caused at a specific positionduring a particular power stroke either before or after thereversal-related apparatus would otherwise cause such ignition. Such apositionresponsive ignition can be used in a case where a singletransitional or running compression stroke might otherwise tend to movethe power piston inwardly beyond the desired optimum inner reversalpoint, or to provide a position ignition in case of unexpected failureof the reversal-related ignition on a particular stroke. If desired, thereversal-related ignition may be used only for the transitional and/orinitial starting strokes, and a position-responsive ignition forsubsequent normal engine operation. Thus the present invention alsoprovides an advantageous combination of selectively operablereversal-related and position-responsive ignition apparatus in a freepiston engine.

For the purposes of the present invention, a reversalrelated ormovement-related power piston characteristic or parameter is definedbroadly to be any characteristic which has a predeterminablerelationship to the moment when the power piston reaches a reversalpoint at the end of a compression stroke, and which is substantiallyindependent of variations in the actual physical position of the pistonwithin its cylinder at the moment of piston reversal for different powerstrokes. Thus one such parameter sensing means gives a signal which isan indication of the movement or rate of change of position of the powerpiston within the free piston engine, as distinguished from the exactphysical position of the piston along its path of movement.

For the purposes of the present invention, a movement-related parameteris to be contrasted with a position-responsive or displacementparameter, which directly indicates the position or displacement of thepower piston. Examples of such displacement parameters are displacementsor positions of parts mechanically linked to the moving power pistonwithin a free piston engine and the displacement or position ofa camfollower riding on a cam surface fixed to the power piston within suchan engine and designed to trigger at a substantially fixed position ineach cycle. Thus the term position-responsive" is used herein incombination with such expressions as characteristic, parameter, ignitionmeans, timing means", combustioncausing means or the like, forconvenience in designating something which takes place at apredetermined location along the path of movement of a freelyreciprocating engine element, without regard to variations in the timeor the physical position at which that engine element reverses directionat the end of a compression stroke.

The term fuel" is used herein in a broad sense to include any gas ormixture of gases customarily used as a combustible charge in a freepiston engine. For example, fuelmay be a combustible gas, a combustiblemixture of gas and air, or a charge of air into which fuel is to beinjected near the end of a compression stroke.

The terms combustion-causing means and ignition means andthe like,areused in a broad sense (except where the context requires aspecificinterpretation) to include such devices as the spark plug and sparkcausing circuitry in a spark ignition engine and the fuel injection of acompression ignition engine, as well as other equivalents to suchdevices.

The term single-acting is used herein in connection with free pistonengines in which a particular power piston and the parts connectedtherewith are driven by successive power strokes in only one direction,as distinguished from double-acting engines in which such parts aredriven by successive alternating power strokes, with a power stroke inone direction followed bya power stroke in the opposite direction insuccessive cycles of operation.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings which form a part ofthis application,

FIG. 1 is a view, with certain parts shown schematically and in section,and with other parts shown in schematic diagram only, of one preferredembodiment of the invention;

FIG. 2 is an enlarged partial sectional view of a modification of oneportion of. the device of FIG. 1, in which a position-responsivetimingmeans for causing the first combustion on the initial startingstroke is automatically moved to an inoperative position for subsequentstrokes, provided the engine starts and continues to run duringtransitional and/or normal operation; and

FIG. 3 is a view, similar to FIG. 1, of another preferred embodiment. 7

It will be understood that the drawings are designed to show theprinciples of operation according to the present invention and are in nosense to be understood as dimensional representations of the actualrelative proportions involved of the parts. Moreover, reference in thefollowing descriptions to left right, or other directions are to beunderstood as referring only for purposes of explanation to the relativedirections as one views the accompanying drawings.

DESCRIPTION OFTHE PREFERRED EMBODIMENT 'In- FIG. I, a combination ofelements according to one preferred form of thepresent invention isshown.

A free piston engine 17 has a power section 18 located at the extremeleft of the engine and has a power piston 20 reciprocating along thelongitudinal central axis of the engine within a power cylinder 21. Thehousing of engine 17 is generally designated at 22. The engine isprovided with conventional means for introducing fuel and exhaustingburnt fuel at.appropriate times in the engine cycle. For illustration,these are shown as respective inlet and exhaust ports 14 and 16 in thewall of cylinder 21.

In this case, an outwardly-compressing compressor 23 is shown by way ofexample at the right end of engine 17. A shaft 24, extends horizontallyalong the longitudinal central axis of engine 17 and interconnects powerpiston 20 and a compressor piston 26. Compressor piston 26 is arrangedto be reciprocally movable between the right face 36 of compressorpiston 26 and the inner face of end wall 38.

A bouncer control valve 37 provides for the control of pressure in achamber 42 formed between the left face 44 of piston 26 and inner wall48. Valve 37 provides for the control of fluid pressure in chamber 42and allows chamber 42 to operate as a negative bounce chamber, i.e., achamber in which compression of fluid during a leftward'compressionstroke of power piston provides additional energy for a power stroke tothe right,'and in which the expansion of volume in chamber 42 during apower stroke to the right provides a realong the central longitudinalaxis of engine 17 within duced pressure or partial vacuum in chamber 42to facilitate the return stroke of pistons 20 and 26 to the left.

A bouncer valve spring 40, which is adjustable as shown schematically at46, can be set to establish a maximum pressure within bounce chamber 42.Higher pressures will then be vented through conduit 87, valve 37 andoutlet 88.

The engine will also include other known features, the details of whichare not essential to an understanding of the present invention. Thus,where shaft 24 penetrates interior walls 48 and 49, conventional shaftseals (not shown) are provided to prevent the leakage of gas andlubricant around shaft 24 as it reciprocates.

To. facilitate an understanding of the starting features according tothepresent invention, a description of additional portions of the completefree piston engine and its associated load device or compressor will behelpful. Thus, during operation, the output from compressor chamber 34is fed through one-way valve 32 into a compressor discharge manifold 52.The discharge manifold has an outlet conduit 53 which communicates witha further conduit 54 connected to a suitable air storage tank orreservoir 56. Communication between conduits 53 and 54 is controlled bya spring loaded discharge valve 57 which has a-loading spring 58normally urging valve 57 to closed position. When the engine startsoperation and sufficient pressure is generated within conduit 53 toovercome the resistance of spring 58, valve 57 can snap to a fully openposition to provide complete communication from conduit 53 to conduit54.-Thus, the output from the compressor will be fed to the storagereservoir-56 or to some other device for which'such output is designed.

In order to relieve the pressure within compressor chamber 34 wheneverthe engine shuts down, and thus facilitate the arrangements for startingthe engine according to the present invention, a manifold pressuredischarge conduit 59 is connected at one end to discharge manifold 52.The other end of conduit 59 is controlled by a valve 61 which is shownin FIG. 1 in its normal operating position in which conduit 59 isclosed. Upward movement of the movable control portion of the valveagainst the urging of spring 62, effectively connects conduit 59 with afurther conduit 63 by means of valve passage 64. Conduit 63 is connectedto the chamber 65 providing a desired back-pressure on the rear side ofvalve 57. Thus when valve passage 64 is moved into upper operatingposition, the pressure within manifold 52, which is already applied tothe upper or front side of valve member 57, will be applied throughconduits 59 and 63 to the rear side of valve 57. With equal pressure oneach side of valve 57, the spring member 58 will immediately becomeeffective to force the valve to closed position. The pressure withinmanifold 52, conduits 59 and 63 and chamber 64 will then gradually berelieved, while valve passage 64 is in its upper position, through asuitable bleed orifice, shown schematically at 66, which communicateswith conduit 63 between valve 61 and chamber 65.

Valve 61 is operated in any suitable manner at the time the engine isshut down, in order to insure closing of outlet valve 57 and thusprevent escape of pressure from receiving reservoir 56 back through themanifold 52. In effect, valve 57 and its associated controls provides aone-way check valve for the output from manifold 52. This check valvehas a positive action in both directions between fully open position inwhich it accommodates the full output of compressor chamber 34, and afully closed position which effectively retains the pressure in receiver56.

Valve 61 may be connected to main ignition switch 67, for example, sothat the valve is moved from the running position of FIG. 1 to its upperbleed position, with passage 64 connecting conduits 59 and 63, whenevermain switch 67 is opened to turn off the ignition. Switch 67 may beopened manually, or in response to predetermined pressure build-up inreservoir 56, or in some other suitable manner.

The present invention includes means to move the power and compressorpistons to a predetermined point in preparation for a desired startingcycle. For this purpose, a three-position valve 68 is provided which maybe axially movable from one position to another and which is normallyheld in the position shown in FIG. 1 by equal and opposed spring means69 and 70. In this normal running position, the central section 72 ofvalve 68 blocks communication between the conduits to be describedbelow, which are used only for positioning the piston assembly prior toand during the starting operation. One incoming valve conduit 73 isconnected by valves shown schematically at 74 and 76 to the pressurereceiver or reservoir 56, or to a suitable source of auxiliary pressure,which need not have the high pressure which is ordinarily found in astorage reservoir such as 56. A reducing valve 77 may be used in conduit73 to provide the desired reduced pressure.

Another conduit 78 on the same side of valve 68 as conduit 73 isconnected so that it is open to atmosphere for relief of desiredpressures as described below.

Valve 68 includes additional valve sections 79 and 81 which providecross connections between the respective conduits 73 and 78 at one sideof the valve, and conduits 82 and 83 at the other side of the valve 68.Conduit 82 is connected at 84 to the compressor chamber 34. Conduit 83is connected at 86 to a conduit 87 connecting the bouncer chamber 42with valve 37 and bouncer outlet 88.

In operation, when engine 17 is shut down and it is desired to positionthe pistons and 26 for a starting cycle, valve 68 is first operated tothe right so that valve section 79 connects conduit 73 with bouncerconduit 83 and thus introduces air under pressure from reservoir 56 andregulator 77 into the conduit 87 and bouncer chamber 42. At the sametime, the valve section 79 also connects conduit 82 to exhaust conduit78. Thus the compressor chamber 34 is effectively connected by acompletely open connection to the atmosphere to relieve any pressure inthat chamber. The resulting difference of pressure between therelatively higher pressure in bouncer chamber 42 and the ambient oratmospheric pressure in compressor chamber 34 forces compressor piston26 and associated parts to the right toward the outer end of compressorcylinder 28.

If valve 68 is now permitted to return at least momentarily to itsnormal position as shown in FIG. 1, the compressor piston and associatedparts will remain in their right hand position for starting.

According to the present invention, the starting is achieved byproviding a suitable combustion chamber, feeding a charge of combustiblegas into it, and then igniting this combustible mixture by a spark.Although this can be done in any suitable combustion chamber, i.e., anyof the cylinders of the engine or even an antechamber to such acylinder, it is preferable to use the regular combustion chamber in thepower cylinder 21. This cylinder has been provided with ignition meansin the form of spark plug 89 and is constructed in any event with thenecessary strength to withstand the pressures and temperatures ofcombustion during normal engine operation. stroke, and of the For astarting cycle according to one embodiment of this invention, the powercylinder 21 is accordingly charged with a combustible mixture which maybe introduced through its inlet port 14. A carburetor or mixer 91 isshown in block diagram and is connected in normal fashion at 92 to aregular gas supply 93. Thus, during normal running of the engine, thecarburetor and gas supply will deliver the desired gas to the powercylinder 21 at the proper times when inlet 14 is open on an outwardmovement of piston 20 at the end of a power stroke to the right.

In order to achieve the starting of the engine according to the presentinvention a special starting valve means 94 is provided. This valve hastwo valve sections 96 and 97. When valve section 96 is in position asshown in FIG. 1 during normal running of the engine, nothing passesthrough valve 94. When the valve is operated to the left, however, itconnects an auxiliary air supply shown schematically at 98 through aconduit 99 through a conduit 101 leading to the carburetor 91. Thedesired connection is made by valve passage 102 in valve section 97.Valve section 97 may also include another passage 103 for connection ofan auxiliary gas supply 104 through conduit 106 and 107 to carburetor91. i

Thus, operation of starter valve 94 to the left is designed to introduceinto the power cylinder 21 an appropriate combustible starting mixtureof gas and air, as needed during the starting cycle. It might be notedat this point that the auxiliary air is necessary to provide acombustible mixture on the initial starting stroke in those cases wherethe free piston engine normally operates with air supplied to the powercylinder or to the mixture by a suitable scavenge system. Such a systemis shown schematically in FIG. 1 with reference to the chamber 107between power piston 20 and inner wall 49. An inlet valve 108 permitsair to enter chamber 107 when the power piston 20 is moving to the left.Then, when the power piston 20 returns to the right, for example duringa power stroke, outlet valve 109 connects the scavenge chamber 107either directly with intake 14 or with mixer 91, depending on the typeof engine arrangement involved. Thus, during normal operation of theengine, the movement of power piston 20 with respect to scavenge chamber107 will provide a sufficient flow of air to properly charge the powercylinder.

Since, however, such a scavenge system provides no air output whenpiston is at rest prior to a start, the present invention, throughstarter valve 94 and auxiliary air supply 98, provides the necessaryproportion of air to achieve a combustible mixture in the power cylinderfor the starting operation.

Thus, a starting cycle for the embodiment of FIG. 1, requires operationof starter valve 94 from the position of FIG. 1 to its left position inwhich section 97 of valve 94 becomes operative to connect the auxiliaryair and gas supplies. At the same time, valve 68 (which has previouslybeen operated to its right-hand position) should now be operated to theleft, so that valve section 81 will connect the low pressure air fromconduit 73 through conduit 82 to the compressor chamber 34 and ventbouncer element chamber 42 to the atmosphere at 78. Thus, the higherpressure in chamber 34 starts movement of compressor piston 26, shaft 24and'power piston 20 to the left in a manner corresponding to itsmovement during a regular compression stroke. The pressure in chamber 34need not be particularly high, however, since it is supplied over therelatively large area of compressor piston 26 and'needs to provide onlya little more force than necessary to overcome the frictional'resistanceof the parts. Thus the unique starting arrangement contemplated by thisinvention can even utilize a manual air pump for air at 73 and 98. Thepressure at 73 may be as low as only 2 p.s.i.g. (pounds per square inchgauge,i.e. above ambient pressure).

As the pistons move to the left, power piston 20 will first move pastthe outer end of inlet port14 and then gradually close this port, aswell as exhaust port 16. As soon as the intake and exhaust ports 14 and16 are substantially closed, or shortly thereafter, the ignition systemis operated to provide a spark at 89 to ignite the combustible mixturein power cylinder 21 and provide a first combustion or power stroke ofpiston 20 to the right. The spark for this initial combustion isprovided in this embodiment by a position-responsive actuator, i.e., anarrangement in which ignition is triggered-at a specific position of thepower piston 29 and associated parts along the path of movement of thepiston. By way of example, a setof breaker points'112 is supported on anadjustable slide 113, which is moveable axially of the engine within aguide slot 114. A manual adjusting knob 116 extends outwardly of thecasing to permit adjustmentof the position at which the contacts will beactuated.

As is customary in the art, one of the breaker points 112 is carried ona movable supporting arm 117, and the other is on a relativelystationary arm 118. An intermediate spring 119 normally urges the pointsapart from each other, and a stop 121 limits the upward movement of themovable contact arm 117. This movable arm carries an actuating portion120 designed for engagement by a timing cam 122, suitably mounted on asupport 123 carried by thepiston shaft 24, or by some other suitableportion of the engine which moves in synchronism with the power piston20. The movable contact is connected in known manner by a suitable wire124 to a junction point 126 in circuit with the positive side of thebattery 127, the negative side of which is grounded at 128. Another wire129 connects the fixed contact through starting switch 136, junction141, and main switch 67, with the primary winding 131 of ignition coil132. The secondary winding 133 of ignition coil 132 is connected at 134to the spark plug 89,

and the respective ignition coil windings 131 and 133 are grounded, asshown, to complete the normal circuit.

In the embodiment of FIG. 1, the starting switch 136 is operated when itis desired to have the breaker points 1 12 in circuit during thatportion of the starting or running of the engine when ignition is to betimed at a particular position of the power piston 20 along its path ofmovement in the power cylinder. In FIG. 1, the power piston 20 is shownat the outer dead point or reversal point of its path with the powerface of the piston at the location indicated by the arrow and dottedline 137. During normal operation itis desirable that the piston move tothe left during a compression stroke, until it reaches a normal innerreversal point indicated by the dotted arrow 138.

According to the present invention, as power piston 20 moves fromposition 137 toward position 138 and the power cylinder 21 is filledwith a suitable combustible mixture through operation of valve 94, thetiming position adjustment at 116 is set initially, so that the breakerpoints will be actuated by cam 122 as the inner power piston facereaches the intermediate point 139 along its path, i.e., some time afterthe intake and exhaust valve ports have been substantially closed, butwithout necessarily waiting until the piston completely reaches itsinner reversal point 138. At this point 139, the combustible mixture in21 will be under substantially less pressure thanthe compression ratioswhich would be customary in regular running of the engine with a fullcompression stroke. The starting movement of piston 20 from right toleft, as already described, is under only the pressure fed by valve 68to chamber 34. Since the area of piston 26 is generally greater thanthat of power piston 20, a given pressure in chamber 34 can produce asomewhat higher pressure in the power cylinder, but the presentinvention requires no particular pressure therein.

In any event, the ignition contacts are set by adjusting member 116 toproduce the initial combustion for a first power stroke of the powerpiston 20 at a point which will surely be reached as the piston movesfrom right to left, without necessarily waiting for the piston tomovefarther to the left than the intermediate point 139. This initiallow compression power stroke will ordinarily provide less force than anormal later power stroke after the engine has been started, but it willbe sufficient to start the reciprocation of the pistons. Ignitionadjustment member 116 may then gradually be moved to the left, so thatsuccessive power strokes are started by combustion at points graduallycloser to the normal desired inner reversal point 138. After the initialcombustion stroke, the movement of power piston 20 will also startoperation of the normal scavenge air system through chamber 107 andvalve 109, so that subsequent combustion can be achieved in more normalmanner by the regular supply of gas through mixer 91 and air from thescavenge system. Thus'valve 94 can be operated back to its right-handposition to cut off the auxiliary gas and air supplies, which areprovided primarily to insure a suitably proportioned combustible mixturefor the initial starting stroke.

In the operation just described, the gradual adjustment of the point ofignition from the starting stroke combustion at piston position 139toward the normal running condition at which combustion occurs closer tothe normal inner reversal point 138 is achieved by adjustment of thephysical location along the path of piston movement at which the sparkignition is provided. According to a further feature of the invention,however, there are special advantages in controlling the initiation ofcombustion, at least during the transition from the first startingstroke to a normal running condition, and preferably also during thenormal running condition by timing the point of ignition at apredetermined moment in time related to the moment when the power pistonactually reverses direction at the end of a compression stroke and thestart of an immediately following power stroke. Such reversalrelatedtiming is independent of variations which may occur in a free pistonengine between the actual physical position of the power piston 20 atthe moment of reversal for different successive power strokes.

For this purpose another set of breaker points 137 is shown in FIG. 1connected in parallel to the breaker points 112. Moveable breaker pointarm 138 has its contact point connected to the junction 126 with thepositive side of battery 127. Fixed breaker point 139 is connected tojunction point 141 in wire 129 leading to the primary winding 131 ofcoil 132. Junction 141 is between the main ignition switch 67 and thestarting switch 136, so that breaker points 137 will be in circuit withprimary winding 131 at all times, whether starting switch 136 is open orclosed. Thus starting switch 136 may be closed for the startingoperation, so that contacts 112 provide the initial position-responsiveignition at sparkplug 89, when piston 20 reaches the preselectedstarting point 139. Switch 136 may then be opened, so that the ignitionpoint for subsequent transitional and running power strokes iscontrolled by breaker points 137. l The making and breaking of thesepoints is controlled by an actuating member 142 of a control means 143,which is designed to make and break the points 137 at a preselected timerelationship to the moment of reversal of power piston 20 at the end ofa compression stroke. The control means shown in FIG. 1 includes acylinder 144 providing a control pressure chamber 146 in which a piston147 connected to output member 142 may reciprocate. Piston 147 is urgedto the left by a spring 148, the tension of which is adjustable by acontrol knob 149, threaded into the endof the cylinder. Thus, when thepressure in chamber 146 increases to a preselected point, determined bythe adjusted force of reference spring 148, the output member 142 willbe urged to the right to cause engagement of the contacts 137. Adecrease in the control pressure 146, at an adjustable time which isrelated to the inner reversal point of the piston, then breaks thecontacts 137 for producing a spark at 89.

Pressure chamber 146 is designed to receive a pressure sensing signalwhich is proportional to a movement-related characteristic or parameterof power piston 20. In this case, pressure'chamber 146 receives pressuresignals through a conduit 151 connected to a pressure sensing cylinder152. A pressure sensing piston 153 moves in cylinder 152 and isconnected at 154 to a member 156 carried by the shaft 24. Thus themovement of sensing piston 153 corresponds to the movement of the powerpiston 20 and generates pressures in cylinder 152 and transmits them tocontrol chamber 146 in predetermined relationship to the velocity and/oracceleration of the power piston 20 along its path. Control means 143may include adjustable timing means which in this embodiment isillustrated by i a controlled orifice 157, which is adjustable as shownschematically at 158. Orifice 157 provides a desired rate of relief ofpressure from control chamber 146 and accordingly times the moment atwhich breaker points 137 separate.

Thus, as power piston 20 moves to the left during a compression strokefrom its outer dead point 137 toward its inner reversal point 138,piston 20 will first accelerate to a maximum velocity at someintermediate point along the path and the velocity will then graduallydecrease. The velocity reaches zero at some point along the path wherethe forces tending to move piston 20 to the left are balanced and thenexceeded by the forces tending to move it to the right. During theinitial acceleration to the left, sensing piston 153 provides a pressuresignal which causes an increase in pressure in control chamber 146faster than the orifice 157 can relieve such pressure. Contacts 137 willthen close. As the piston 20 slows down on its leftward stroke justprior to reversal, however, the rate of input of the pressure signalfrom piston 153 decreases. The orifice 157 can then relieve the pressurein chamber 146 to cause breaking of the contacts at 137. Thus byappropriate adjustment of the spring tension at 148 and the orifice sizeat 157, breaker points 137 can be closed and opened to provide a sparkat 89 in the desired predetermined time relationship at or about thetime that the power piston 20 reverses direction. This timing will takeplace, whether the piston, at the time of reversal, is close to thenormal operating inner reversal point 138 or whether it is close to thestarting point 139 or somewhere else along its path within the operatingrange of the parts.

The breaker pointsl12 may be effectively disconnected and kept fromcausing premature ignition after the first starting combustion, byopening manual starting switch 136 so that the control system 143 andbreaker points 137 can take over the subsequent ignition in relation tothe inner reversal points of the power piston 20. Alternatively, sincethe adjustment of member 116 in slot 114 permits movement of thecontacts to the left, the contact points 112 can be moved far enough toprevent engagement of the cam 122 with member 120, even when powerpiston 20 reaches its normal inner reversal point 138. This willeffectively disable or inactivate the position-responsive ignition means112.

Still another embodiment for effectively disabling the breaker points112 after the first starting combustion is shown in FIG. 2. In thiscase, instead ofa fixed cam 122 on member 123 connected to piston shaft24, the member 123A, FIG. 2, is provided with a movable timing camportion 161 at the end of a mass 162, supported for sliding movementwithin a guide channel 163 in member 123A. A spring 164 normally urgesmass 162 to the position shown in FIG. 2 in which cam portion 161 willproject far enough to actuate the portion 129 of breaker points 112 inthe same manner described for fixed cam 122 of FIG. 1. Thus, during theinitial compression stroke, which is at relatively low velocity ofmovement from right to left, mass 162 will remain in the relativeposition shown, and the initial spark will be provided at the desiredpower piston position 139 of FIG. 1.

If ignition is successful, the power piston 20 will then be acceleratedsharply to the right during the initial power stroke. The inertia ofmass 162 will urge it against spring 164 to a relatively retractedposition, in which cam portion 161 will not project far enough to engagethe portion 120 on subsequent strokes. To keep the cam portion 161 inits retracted position as long as the piston assembly is beingaccelerated rapidly in successive power strokes, the mass 162 isconnected by shaft 166 to a plunger 167 in an auxiliary cylinder orchamber 168. Plunger 167 and cylinder 168 provide a dash-pot or dampereffect. A large opening 169 at the right end of cylinder 168 permits theentrance of air and facilitates movement of plunger 167 to the left,when the acceleration of the power stroke causes relative movement ofmass 162 and associated parts in that direction. This movement isfurther permitted by the one-way valve 171 at the left end of dash-potcylinder 168, which permits rapid escape of air at the left of plunger167. Check valve 171, does not, however, permit the entrance of suchair, which can only be restored through a small bleed orifice 172. Thesize of this orifice is so chosen that the rate of return movement ofplunger 167, shaft 166 and mass 162 from left to right under the urgingof spring 164 will be too slow to project cam portion 161 betweensuccessive power strokes in which combustion is successfully achieved.If, however, the engine is stopped, either intentionally or otherwise,then the continued entrance of air through orifree 172 permits spring164 to restore the parts to the position shown in FIG. 2, so that camportion 161 will be ready to actuate breaker points 112 for anotherstarting stroke in a new starting cycle. A further embodiment of theinvention is shown in H6. 3 in which a preferred form ofreversal-related control apparatus for spark ignition is operativelyconnected in a manner designed to control ignition both on an initialstarting stroke and during the transition from the first starting stroketo a normal running condition, as well as during the transition from thefirst starting stroke to a normal running condition, as well as duringthe ultimate normal running operation of the engine.

In this case, a modified starting mixture control valve 94A is used.Instead of controlling the flow of both auxiliary gas and air to themixer and power cylinder for the starting stroke and then stopping suchflow when the regular gas supply and scavenge air systems handle the.subsequent power strokes, the valve 94A'changes only the auxiliary airsupply and connects the regular gas supply to the mixing valve 91 inboth positions of valve 94A. Auxiliary air is provided byvalve section97 during starting, until the usual scavenge air system provides enoughair. The auxiliary air is then discontinued by section 96A of valve 94A.Both valve sections 96A and 97 keep the gas supply connected to themixer, not only for the starting power stroke, but also duringtransition and normal running of the engine.

This preferred control mechanism 174 utilizes the principle of balancingdynamic pressures above and below a moveable diaphram to control theignition breaker points 137. For this purpose the control unit isconnected to receive the pressure signals from conduit 151, as generatedby sensing piston 153 in response to velocity and acceleration of thepower piston 20. Conduit 151 feeds its pressure signals to branches 176and 177 which are connected to respective lower and upper pressurechambers 178 and 179 located below and above a flexible diaphram 181suitably supported in a housing 182. A controlled exhaust orifice 183,the effective opening of which may be adjusted as shown schematically at184, is connected to the lower chamber 178. Another open exhaust conduitat 186 is connected to the upper chamber 179.

The center portion of flexible diaphram 181 is secured to an operatingshaft 187 which extends vertically upward to serve as an output memberfor actuating the breaker points 137. A collar 188 secured to shaft 187engages a stop 189 to limit the downward movement of the shaft 187 andestablish a rest position for diaphragm 181. The parts are helddownwardly in this position by a relatively light spring 191, thetension of which may be adjusted by a threaded knob or collar member192. The upper end 193 of shaft 187 has a telescoping resilient overrideconnected at 194 with the contact actuating member 196. Member 196causes engagement of breaker points 138 and 139 when the shaft 187 anddiaphram 181 are moved upwardly and then opens the contacts when thediaphram and shaft move back down.

In operation, when power piston is moved slowly to the left in themanner described in connection with FIG. 1 in order to achieve initialcombustion, the increasing pressure signal fed through conduit 151 willbe distributed both above and below diaphragm 181. The more restrictedorifice 183 below diaphragm 181, however, causes a relative pressuredifferential, so that the pressure below the diaphragm exceeds thatabove the diaphragm. Thus shaft 187 is moved upwardly to causeengagement of the breaker points. As power piston 20 moves farther tothe left and reaches approximately the desired point of initialignition, even the slight compression within the power cylinder 21 willslow the movement of power piston to the left. As this movement slowsdown, the relief of pressure from the orifice 183 exceeds the decreasedinput at 176 and soon equalizes the pressure below and above diaphragm181. Shaft 187 is then urged downwardly by spring 191 to open thebreaker points at 137 and cause the initial spark.

In this embodiment, for the operation just described, it will beunderstood that the contact points 112 will be either omitted entirely,or moved far enough to the left so that they will not be actuated, i.e.,so that cam 122 will not reach actuating portion 120.

The same type of action just described for the first starting strokewill occur during the transitional firing strokes, as the pistonmovement gradually builds up to its desired normal strength length,except that the action will be more rapid. in this more rapid action, incase the bleed action of restricted orifice 183 is not sufficient tolower the pressure in chamber 178 before the power piston reaches itsreversal point, the diaphragm will at least be moved suddenly downwardlyto open the breaker points no later than a point immediately after thereversal of the inner dead point. At this point, with sensing piston 153beginning to move to the right, the pressure in conduit 151 and inbranches 176 and 177 will be rapidly reduced. This reduction will bemore effective, however, in lower chamber 178, since the rate ofpressure removal through conduit 176 cannot be equalled by the returnmovement of air in through the restricted orifice at 183 as rapidly asthe pressures within the upper chamber 179 may be restored through thegreater opening of conduit 186. Thus there will be a sudden positivedownward movement of the diaphragm 181 and shaft 187, until stops 188and 189 engage each other. Thus, depending on the actual adjustment at184 of orifice 183, the spark can be caused to occurjust prior to, at,or no later than immediately after the reversal of the power piston atits inner reversal point, i.e., the end of a compression stroke and thestart of a new power stroke. Thus the entire operation of starting theengine, passing through a transitional stage of gradually lengtheningpower strokes, and then running at normal operation'with pistonreversals at or near the normal desired inner dead point, can all beachieved with the control unit 174.

Although breaker points 112 could be omitted entirely, as previouslymentioned, they have been retained in the embodiment of FIG. 3, so thatthe device of FIG. 3 can again use a combination of positionresponsiveignition means, and reversal-related ignition means. For example, bysetting contacts 112 at its extreme left position in FIG. 3, cam 122will always actuate these breaker points at, or even slightly beyond,the desired inner reversal point of piston 20. Thus the breaker points112 can be set to correct what might otherwise be too long a compressionstroke to the left resulting from some abnormality in operation of theengine. Points 112 then provide ignition no later than the point atwhich cam 122 engages operator 120, in case the piston might nototherwise reverse direction, until it had penetrated slightly fartherinto the head of the power cylinder.

Thus, as described above, the present invention is capable ofutilization in several forms, in each of which the timing of combustionin predetermined time relationship to the moment of reversal of thepower piston at the end of the compression stroke provides advantageousoperation during at least the transitional period between the firststarting stroke and the achievement of normal running conditions. In thedevice of FIG. 1, this reversal-related control of ignition is combinedwith a position-responsive ignition control, and the latter is used tocontrol the initial spark for the first power stroke during the startingcycle. In the embodiment of FIG. 3, the position-responsive set ofbreaker points 112 may either be omitted or disconnected completely onthe one hand, or may be utilized in combination with thereversal-related ignition control 174 to correct special situations inwhich the reversal-related system might provide a spark somewhat laterthan desired or might unexpectedly fail to provide a spark at all.

The principles of the invention can be carried out with a wide varietyof psecific embodiments which may differ from those shown in FIGS. 1 to3 in ways which will be readily apparent to those skilled in the art.For example, other types of reversal-related control units responsive toa power piston movement-related characteristic may be utilized inaddition to systems based on the sensing of pressure. Other fluidcontrol systems, as well as electrical or mechanical equivalents theretocan be used to achieve the desired starting cycle, the preferred controlof the transition from initial starting combustion to a runningcondition, and the ultimate timing of ignition during normal operationof such a free piston engine.

The foregoing specification has accordingly set forth the nature andprinciples of the present invention together with illustrativevariations in the preferred embodiments by which the invention may bepracticed.

Now, therefore, what is claimed is:

1. In a free piston engine having a power cylinder with inlet andexhaust ports operable between closed and open positions in desirednormal operating sequence, a power piston reciprocally movable in thepower cylinder along a path between desired normal inner and outerpiston reversal points which may vary from stroke to stroke, means forcausing repetitive combustion in said power cylinder to drive said powerpiston during normal engine operation, at least one other cylinder, asecond piston movable therein, and means interconnecting said power andsecond pistons for simultaneous reciprocal movement in their respectivecylinders, the improved starting means comprising, in combination,piston-moving means for moving the power piston inwardly toward itsdesired normal inner reversal point from an outer preliminary startingposition to an intermediate first relative position of the pistons atwhich the pressure in the power cylinder is substantially below thecompression pressure customary in the power cylinderjust prior tocombustion during normal engine operation, means defining a startingcombustion chamber in connection with one of said cylinders, means forsupplying a combustible starting mixture to said starting combustionchamber before the pistons reach said intermediate position, spark meansfor igniting said starting mixture within the starting combustionchamber, and means for initially energizing said spark means as saidpiston-moving means moves said pistons to said intermediate firstrelative position and thereby causing combustion of the combustiblestarting mixture, the energy released by said starting mixturecombustion being transmitted to one of said pistons to start rapidreciprocal movement of the power piston toward its outer desiredreversal point and thereby initiate normal engine operation, and saidmeans for causing repetitive combustion in said power cylinder duringnormal engine operation being thereafter operable to cause suchcombustion at other relative intermediate positions of the power pistonat which a combustible mixture is under gradually higher and more normalcompression pressures within the power cylinder during transitionaloperation while the engine is assuming normal operating condition and atthe desired normal inner reversal point during such normal engineoperation.

2. A free piston engine according to claim 1 in which said startingcombustion chamber is within the power cylinder and includes the portionof the power cylinder which serves as a power chamber for repetitivecombustion to drive said power piston during normal engine operation.

3. A free piston engine according to claim 2 in which said means forcausing repetitive combustion during normal engine operation includessaid spark means, and reversal-related control means for energizing saidspark means during the compression strokes of the power piston duringtransitional and normal operation and independently of any specificposition of the power piston along its path of movement within the powercylinder.

4. In a free piston engine having a power cylinder with fuel inlet meansand exhaust means operable between closed and open positions in desirednormal operating sequence, a power piston reciprocally movable in thepower cylinder along a path between desired normal inner and outerpiston reversal points which may vary from stroke to stroke, means forcausing repetitive combustion in said power cylinder to drive said powerpiston during normal engine operation, at least one other cylinder, asecond piston movable therein, and means interconnecting said power andsecond pistons for simultaneous reciprocal movement in their respectivecylinders, the improved starting means comprising, in combination, meansdefining a starting combustion chamber in connection with one of saidcylinders, means for supplying a combustible starting mixture to saidstarting combustion chamber, spark means for igniting said startingmixture within the chamber, and means for initially energizing saidspark means at a first relative position of the pistons at which thepressure of the mixture in said starting chamber is substantially belowthe compression ratio customary during normal running of such enginesand thereby cuasing combustion expansion ofthe combustible mixture, theenergy released by said cumbustion expansion being transmitted to one ofsaid pistons to start rapid reciprocal movement of the power pistontoward its outer desired reversal point and thereby initiate normalengine operation, and said means for causing repetitive combustion insaid power cylinder being operable to cause such combustion at otherrelative positions of the pistons at which a combustible mixture isunder substantially higher and more normal compression pressures withinthe power cylinder during transitional operation while the engine isassuming normal operating conditions and during normal engine operation,said starting combustion chamber beingwithin the power cylinder andincluding the portion of the power cylinder which serves as a powerchamber for repetitive combustion to drive said power piston duringnormal engine operation, and said free piston engine having means formoving said pistons to a preliminary starting position within theirrespective cylinders prior to operation of the means for initiallyenergizing said spark means, and means for moving said power pistontoward its inner reversal point from said preliminary starting positionto said first relative position at which the spark means is initiallyenergized, said preliminary starting position being close to the outerdesired reversal point of the power piston and said first relativeposition of the piston being an intermediate position in which the inletand exhaust means are substantially closed and the combustion gasesexert a substantial pressure against the power piston when ignited anddrive the power piston in the direction of its desired power stroke.

5. A free piston engine according to claim 4 in which said startingmeans is responsive to air at pressure as low as only 2 p.s.i.g. (poundsper square inch gauge, above ambient pressure) to move the pistons fromtheir preliminary starting position to said first relative position.

6. In a free piston engine having a power cylinder with fuel inlet meansand exhaust means operable between closed and open positions in desirednormal operating sequence, a power piston reciprocally movable in'thepower cylinder along a path between desired normal inner and outerpiston reversal points which may vary from stroke to stroke, means forcausing repetitive combustion in said power cylinder to drive said powerpiston during normal engine operation, at least one other cylinder, asecond piston movable therein, and means interconnecting said power andsecond pistons for simultaneous reciprocal movement in their respectivecylinders, the improved starting means comprising,

in combination, means defining a starting combustion chamber inconnection with one of said cylinders, means for supplying a combustiblestarting mixture to said starting combustion chamber, spark means forigniting said starting mixture within the chamber, and means forinitially energizing said spark means at a first relative position ofthe pistons at which the pressure of the mixture in said startingchamber is substantially below the compression ratio customary duringnormal running of such engines and thereby causing combustion expansionof the combustible mixture, the energy released by said combustionexpansion being transmitted to one of said pistons to start rapidreciprocal movement of the power piston toward its outer desiredreversal point and thereby initiate normal engine operation, and saidmeans for causing repetitive combustion in said power cylinder beingoperable to cause such combustion at other relative positions of thepistons at which a combustible mixture is under substantially higher andmore normal compression pressures within the power cylinder duringtransitional operation while the engine is assuming normal operatingconditions and during normal engine operation, said starting combustionchamber being within the power cylinder and including the portion of thepower cylinder which serves as a power chamber for repetitive combustionto drive said power piston during normal engine operation, and said freepiston engine having piston positioning means for moving the powerpiston inwardly toward its desired inner reversal point from apreliminary starting position located outwardly beyond said firstrelative position, and fuel delivery means having a member operablebetween a starting position in which the fuel delivery means feeds acombustible auxiliary starting mixture to the power cylinder and arunning position in which the fuel delivery means feeds a normaloperating mixture to the power cylinder, said fuel delivery means memberbeing selectively operable to its starting position, before said pistonpositioning means moves the power piston inwardly to said first relativeposition.

7. A free piston engine according to claim 6 in which the pistonpositioning means includes valve means having a first port forconnection to a source of air pressure, a second port connected to theother cylinder for selectively admitting air to one end of that cylinderand thereby moving the second piston and power piston toward the innerreversal point and toward said first relative position, and a valvemember movable between at least a normal running position in which thevalve member prevents the passage of air from the first port to thesecond port and a starting position in which the valve member connectsthe first and second ports.

8. In a free piston engine comprising a power cylinder having fuel inletmeans and exhaust means, a power piston freely reciprocable in thecylinder along a path between desired normal inner and outer pistonreversal points which may vary from stroke to stroke, and means forcausing repetitive combustion in the power cylinder to drive the powerpiston outwardly toward its outer desired reversal point in successivepower strokes, the improved starting and ignition means comprising meansfor feeding a combustible starting mixture to said fuel inlet means andpower cylinder, means for moving the power piston inwardly toward itsdesired inner reversal point from a preliminary starting position spacedalong its path outwardly of the inner reversal point, and means forinitially igniting said starting mixture within the power cylinder whenthe moving means has moved the power piston inwardly from thepreliminary starting position to a first relative position of the powerpiston at which the pressure of the starting mixture is substantiallybelow the compression pressure customary during normal running of suchengines.

9. A free piston engine according to claim 8 in which at least one ofthe means for causing repetitive combustion and the means for initiallyigniting said starting mixture is a reversal-related means.

10. A free piston engine according to claim 9 in which the means forcausing repetitive combustion is a reversal-related combustion causingmeans.

11. A free piston engine according to claim 10 in which the means forinitially igniting said starting mixture is a position-responsiveignition means.

12. A free piston engine according to claim 1 1 having disabling meansfor discontinuing effective operation of said position-responsive meansafter the initial actuation of the ignition means.

13. A free piston engine according to claim 12 in which said disablingmeans includes a cam-supporting housing operatively connected to movewith the power piston, and an acceleration responsive cam supported insaid housing for movement between a normal starting position in whichthe cam is effective to actuate the ignition means and a retractedposition in which the cam is withdrawn from its effective startingposition, and means automatically moving the cam to retracted positionin response to acceleration of the piston during a combustion powerstroke.

14. A free piston engine according to claim 8 in which each of the meansfor causing repetitive combustion and the means for initially ignitingthe starting mixture is a reversal-related means.

15. A free piston engine according to claim 8 having reversal-relatedmeans operatively connected to each of the means for causing repetitivecombustion and the means for initially igniting the starting mixture,said engine also having position-responsive means operatively connectedto the means for causing repetitive combustion and actuating the meansfor causing repetitive combustion at a predetermined power pistonposition close to the desired inner reversal point independently of theaction of the reversal-related means.

16. The method of starting a free piston engine having a power cylinderwith inlet and exhaust ports, a power piston freely reciprocable in thecylinder along a path between desired normal inner and outer pistonreversal points which may vary from stroke to stroke- ,and adjustablecombustion-causing means for igniting a combustible mixture in the powercylinder and causing successive power strokes ofthe piston toward itsouter reversal point, comprising the steps of a. feeding into the powercylinder a combustible starting mixture capable of ignition at pressuressubstantially below the normal compression pressures of such an engine,

b. moving the power piston toward its inner reversal point to anintermediate position along its path at which the inlet and exhaustports are at least substantially closed; and

c. igniting the combustible starting mixture as the piston moves to theintermediate position and thereby providing a combustion force causinginitial movement of the power piston toward the normal outer pistonreversal point to start the engine.

17. The method ofclaim 16 including the further step of adjusting saidcombustion-causing means after first igniting the starting mixture, andthereby causing combustion for successive transitional power strokes atpoints gradually shifting from said intermediate position toward thedesired normal inner piston reversal point, until the combustion-causingmeans is causing normal operation of the engine.

1. In a free piston engine having a power cylinder with inlet andexhaust ports operable between closed and open positions in desirednormal operating sequence, a power piston reciprocally movable in thepower cylinder along a path between desired normal inner and outerpiston reversal points which may vary from stroke to stroke, means forcausing repetitive combustion in said power cylinder to drive said powerpiston during normal engine operation, at least one other cylinder, asecond piston movable therein, and means interconnecting said power andsecond pistons for simultaneous reciprocal movement in their respectivecylinders, the improved starting means comprising, in combination,piston-moving means for moving the power piston inwardly toward itsdesired normal inner reversal point from an outer preliminary startingposition to an intermediate first relative position of the pistons atwhich the pressure in the power cylinder is substantially below thecompression pressure customary in the power cylinder just prior tocombustion during normal engine operation, means defining a startingcombustion chamber in connection with one of said cylinders, means forsupplying a combustible starting mixture to said starting combustionchamber before the pistons reach said intermediate position, spark meansfor igniting said starting mixture within the starting combustionchamber, and means for initially energizing said spark means as saidpiston-moving means moves said pistons to said intermediate firstrelative position and thereby causing combustion of the combustiblestarting mixture, the energy released by said starting mixturecombustion being transmitted to one of said pistons to start rapidreciprocal movement of the power piston toward its outer desiredreversal point and thereby initiate normal engine operation, and saidmeans for causing repetitive combustion in said power cylinder duringnormal engine operation being thereafter operable to cause suchcombustion at other relative intermediate positions of the power pistonat which a combustible mixture is under gradually higher and more normalcompression pressures within the power cylinder during transitionaloperation while the engine is assuming normal operating condition and atthe desired normal inner reversal point during such normal engineoperation.
 2. A free piston engine according to claim 1 in which saidstarting combustion chamber is within the power cylinder and includesthe portion of the power cylinder which serves as a power chamber forrepetitive combustion to drive said power piston during normal engineoperation.
 3. A free piston engine according to claim 2 in which saidmeans for causing repetitive combustion during normal engine operationincludes said spark means, and reversal-related control means forenergizing said spark means during the compression strokes of the powerpiston during transitional and normal operation and independently of anyspecific position of the power piston along its path of movement withinthe power cylinder.
 4. In a free piston engine having a power cylinderwith fuel inlet means and exhaust means operable between closed and openpositions in desired normal operating sequence, a power pistonreciprocally movable in the power cylinder along a path between desirednormal inner and outer piston reversal points which may vary from stroketo stroke, means for causing repetitive combustion in said powercylinder to drive said power piston during normal engine operation, atleast one other cylinder, a second piston movable therein, and meansinterconnecting said power and second pistons for simultaneousreciprocal movement in their respective cylinders, the improved startingmeans comprising, in combination, means defining a starting combustionchamber in connection with one of said cylinders, means for supplying acombustible starting mixture to said starting combustion chamber, sparkmeans for igniting said starting mixture within the chamber, and meansfor initially energizing said spark means at a first relative positionof the pistons at which the pressure of the mixture in said startingchamber is substantially below the compression ratio customary duringnormal running of such engines and thereby cuasing combustion expansionof the combustible mixture, the energy released by said cumbustionexpansion being transmitted to one of said pistons to start rapidreciprocal movement of the power piston toward its outer desiredreversal point and thereby initiate normal engine operation, and saidmeans for causing repetitive combustion in said power cylinder beingoperable to cause such combustion at other relative positions of thepistons at which a combustible mixture is under substantially higher andmore normal compression pressures within the power cylinder duringtransitional operation while the engine is assuming normal operatingconditions and during normal engine operation, said starting combustionchamber being within the power cylinder and including the portion of thepower cylinder which serves as a power chamber for repetitive combustionto drive said power piston during normal engine operation, and said freepiston engine having means for moving said pistons to a preliminarystarting position within their respective cylinders prior to operationof the means for initially energizing said spark means, and means formoving said power piston toward its inner reversal point from saidpreliminary starting position to said first relative position at whichthe spark means is initially energized, said preliminary startingposition being close to the outer desired reversal point of the powerpiston and said first relative position of the piston being anintermediate position in which the inlet and exhaust means aresubstantially closed and the combustion gases exert a substantialpressure against the power piston when ignited and drive the powerpiston in the direction of its desired power stroke.
 5. A free pistonengine according to claim 4 in which said starting means is responsiveto air at pressure as low as only 2 p.s.i.g. (pounds per square inchgauge, above ambient pressure) to move the pistOns from theirpreliminary starting position to said first relative position.
 6. In afree piston engine having a power cylinder with fuel inlet means andexhaust means operable between closed and open positions in desirednormal operating sequence, a power piston reciprocally movable in thepower cylinder along a path between desired normal inner and outerpiston reversal points which may vary from stroke to stroke, means forcausing repetitive combustion in said power cylinder to drive said powerpiston during normal engine operation, at least one other cylinder, asecond piston movable therein, and means interconnecting said power andsecond pistons for simultaneous reciprocal movement in their respectivecylinders, the improved starting means comprising, in combination, meansdefining a starting combustion chamber in connection with one of saidcylinders, means for supplying a combustible starting mixture to saidstarting combustion chamber, spark means for igniting said startingmixture within the chamber, and means for initially energizing saidspark means at a first relative position of the pistons at which thepressure of the mixture in said starting chamber is substantially belowthe compression ratio customary during normal running of such enginesand thereby causing combustion expansion of the combustible mixture, theenergy released by said combustion expansion being transmitted to one ofsaid pistons to start rapid reciprocal movement of the power pistontoward its outer desired reversal point and thereby initiate normalengine operation, and said means for causing repetitive combustion insaid power cylinder being operable to cause such combustion at otherrelative positions of the pistons at which a combustible mixture isunder substantially higher and more normal compression pressures withinthe power cylinder during transitional operation while the engine isassuming normal operating conditions and during normal engine operation,said starting combustion chamber being within the power cylinder andincluding the portion of the power cylinder which serves as a powerchamber for repetitive combustion to drive said power piston duringnormal engine operation, and said free piston engine having pistonpositioning means for moving the power piston inwardly toward itsdesired inner reversal point from a preliminary starting positionlocated outwardly beyond said first relative position, and fuel deliverymeans having a member operable between a starting position in which thefuel delivery means feeds a combustible auxiliary starting mixture tothe power cylinder and a running position in which the fuel deliverymeans feeds a normal operating mixture to the power cylinder, said fueldelivery means member being selectively operable to its startingposition, before said piston positioning means moves the power pistoninwardly to said first relative position.
 7. A free piston engineaccording to claim 6 in which the piston positioning means includesvalve means having a first port for connection to a source of airpressure, a second port connected to the other cylinder for selectivelyadmitting air to one end of that cylinder and thereby moving the secondpiston and power piston toward the inner reversal point and toward saidfirst relative position, and a valve member movable between at least anormal running position in which the valve member prevents the passageof air from the first port to the second port and a starting position inwhich the valve member connects the first and second ports.
 8. In a freepiston engine comprising a power cylinder having fuel inlet means andexhaust means, a power piston freely reciprocable in the cylinder alonga path between desired normal inner and outer piston reversal pointswhich may vary from stroke to stroke, and means for causing repetitivecombustion in the power cylinder to drive the power piston outwardlytoward its outer desired reversal point in successive power strokes, theimproved starting and ignition means comprising meAns for feeding acombustible starting mixture to said fuel inlet means and powercylinder, means for moving the power piston inwardly toward its desiredinner reversal point from a preliminary starting position spaced alongits path outwardly of the inner reversal point, and means for initiallyigniting said starting mixture within the power cylinder when the movingmeans has moved the power piston inwardly from the preliminary startingposition to a first relative position of the power piston at which thepressure of the starting mixture is substantially below the compressionpressure customary during normal running of such engines.
 9. A freepiston engine according to claim 8 in which at least one of the meansfor causing repetitive combustion and the means for initially ignitingsaid starting mixture is a reversal-related means.
 10. A free pistonengine according to claim 9 in which the means for causing repetitivecombustion is a reversal-related combustion causing means.
 11. A freepiston engine according to claim 10 in which the means for initiallyigniting said starting mixture is a position-responsive ignition means.12. A free piston engine according to claim 11 having disabling meansfor discontinuing effective operation of said position-responsive meansafter the initial actuation of the ignition means.
 13. A free pistonengine according to claim 12 in which said disabling means includes acam-supporting housing operatively connected to move with the powerpiston, and an acceleration responsive cam supported in said housing formovement between a normal starting position in which the cam iseffective to actuate the ignition means and a retracted position inwhich the cam is withdrawn from its effective starting position, andmeans automatically moving the cam to retracted position in response toacceleration of the piston during a combustion power stroke.
 14. A freepiston engine according to claim 8 in which each of the means forcausing repetitive combustion and the means for initially igniting thestarting mixture is a reversal-related means.
 15. A free piston engineaccording to claim 8 having reversal-related means operatively connectedto each of the means for causing repetitive combustion and the means forinitially igniting the starting mixture, said engine also havingposition-responsive means operatively connected to the means for causingrepetitive combustion and actuating the means for causing repetitivecombustion at a predetermined power piston position close to the desiredinner reversal point independently of the action of the reversal-relatedmeans.
 16. The method of starting a free piston engine having a powercylinder with inlet and exhaust ports, a power piston freelyreciprocable in the cylinder along a path between desired normal innerand outer piston reversal points which may vary from stroke tostroke,and adjustable combustion-causing means for igniting acombustible mixture in the power cylinder and causing successive powerstrokes ofthe piston toward its outer reversal point, comprising thesteps of a. feeding into the power cylinder a combustible startingmixture capable of ignition at pressures substantially below the normalcompression pressures of such an engine, b. moving the power pistontoward its inner reversal point to an intermediate position along itspath at which the inlet and exhaust ports are at least substantiallyclosed; and c. igniting the combustible starting mixture as the pistonmoves to the intermediate position and thereby providing a combustionforce causing initial movement of the power piston toward the normalouter piston reversal point to start the engine.
 17. The method of claim16 including the further step of adjusting said combustion-causing meansafter first igniting the starting mixture, and thereby causingcombustion for successive transitional power strokes at points graduallyshifting from said intermediate position toward the desired normal innerPiston reversal point, until the combustion-causing means is causingnormal operation of the engine.